From rwo Thu Feb 19 13:21:37 2004 To: Eric.P.Smith@hq.nasa.gov, Michael.Dopita@anu.edu.au, Mike.Disney@astro.cf.ac.uk, Rogier.Windhorst@asu.edu, awalker@noao.edu, balick@astro.washington.edu, blades@stsci.edu, bond@stsci.edu, calzetti@stsci.edu, dleckrone@hst.nasa.gov, ec@cobi.gsfc.nasa.gov, eyoung@as.arizona.edu, fparesce@eso.org, ger@hokupa.ifa.hawaii.edu, hall@ifa.hawaii.edu, hartig@stsci.edu, hill@buckeyball.gsfc.nasa.gov, holtz@nmsu.edu, inr@stsci.edu, j.silk1@physics.ox.ac.uk, jennifer.wiseman-1@nasa.gov, jfrogel@hq.nasa.gov, jtt@bb4.jpl.nasa.gov, kimble@ccd.gsfc.nasa.gov, lupie@stsci.edu, macchetto@stsci.edu, mackenty@stsci.edu, marcella@phys.ethz.ch, mauro@stsci.edu, mmoore3@hq.nasa.gov, mstiavel@stsci.edu, pbenvenu@eso.org, pmc2@ociw.edu, robberto@stsci.edu, saha@noao.edu, svwb@stsci.edu, tpham@hst.nasa.gov, whitmore@stsci.edu Subject: WFC3 SOC RESOLUTIONS Feb 04 Content-Length: 10033 19 February 2004 RESOLUTIONS FROM WFC3 SOC FEBRUARY 2004 MEETING =============================================== The meeting took place three weeks after Administrator O'Keefe announced the cancellation of HST Servicing Mission 4 by the Space Shuttle. In the absence of servicing, it is expected that critical components within HST will fail such that science operations will have to cease within about 30 months (50% probability). The project and STScI are exploring techniques for extending operations using fewer than the nominal complement of 3 gyros. Before HST's orbit decays, a robot propulsion module will be sent to attach to HST and accomplish a safe de-orbit. Integration and test activities for WFC3 continue at GSFC and Ball. The instrument performs beautifully and meets or exceeds specifications in almost all areas tested to date. SOC is very impressed by the performance of the instrument and congratulates the project team for its exemplary work. It is planned to bring engineering activities to a conclusion within about 6 months. Its engineering status and performance will be fully documented, and the instrument will be placed in safe storage. SOC was asked by the project and by NASA Headquarters for its views on priorities for the close-out period and on possible uses of WFC3 in missions other than HST. 1) PRIORITIES FOR WFC3 CLOSEOUT ACTIVITIES SOC strongly endorses the project's plan ("Fast Track to Thermal-Vac") for the WFC3 close-out process. The main guidelines are these: (i) taking no short cuts which would preclude deployment on a reasonable schedule if SM4 is resurrected; (ii) completing all critical science characterizations, including the IR channel; (iii) retiring the major known development risks which are not specific to HST deployment; and (iv) maximizing the value of WFC3 as an asset potentially available for other NASA missions within a reasonable cost. SOC believes it is imperative to carry this plan to completion. Two specific performance issues arose during testing of the UVIS channel: (a) Reflection ghosts appeared at greater than the 0.5% level in 10 of the 63 filters, including the high priority filters F218W, 225W, 275W, 300X, 658N. Fainter ghosts appeared in F606W. However, these were starlike, and that would be very undesirable in what would be one of the most heavily used filters. In view of the importance of these filters to the core performance of WFC3 in HST or any other likely imaging mission, SOC believes it is essential to resolve the ghost problem before closeout, presumably by securing and verifying new filter designs. (b) Low-level (a few DN) crosstalk appears in the UVIS data, similar, though more pronounced, to effects which have been observed in ACS. Several inexpensive methods to mitigate the crosstalk are being explored and will benefit ACS as well as WFC3. Again, SOC believes it is essential to resolve the crosstalk problem before closeout 2) DEPLOYMENT OF WFC3 The Hubble Space Telescope has been NASA's most prominent and successful scientific endeavor, second only to Apollo as NASA's signature mission. The investments made in HST, including the servicing missions, have been repaid many times over in both scientific return and public interest in and support for space science. A key to HST's success has been its simultaneous access to the crucial ultraviolet, optical, and near-infrared spectral bands. These bands contain the most information about the physics of the universe, and HST is unique in its access to and performance in them. No existing or planned telescope, on the ground or in space, will supersede HST's high resolution, wide field imaging capabilities in the 0.12-1.0 micron band in the foreseeable future. WFC3 was specifically designed to exploit HST's unique capabilities. It is intended for panchromatic (0.2-1.7 micron), wide-field, high resolution imaging with an unusually large filter complement. Among the key scientific problems to which WFC3 would have made major contributions when deployed on HST are these: o Tracing the evolution of dark energy in the universe by obtaining high precision light curves for distant supernovae at redshifts over 1. The nature of dark energy is widely considered to be the most important problem facing contemporary physics. o Establishing the history of star formation in the local universe through panchromatic mid-UV to IR imaging of nearby galaxies and clusters of galaxies. o Exploiting discoveries from the ongoing GALEX and Spitzer Space Telescope missions. These offer unprecedented sensitivity in UV surveys and the mid-far IR domain, respectively. But WFC3, with an optical-UV areal resolution that is thousands of times better than either of these, would be essential in many cases to capitalizing on the results of these missions. Chandra is now predicted to outlive HST by several years and will not have the benefit of coordinated observations even with existing HST instruments. o Exploring formation mechanisms for brown dwarfs through a census of low mass star populations in nearby star formation regions. o Using Lyman dropouts to identify galaxies and proto-galaxies during the reionization epoch in the early universe, which is now thought to be at redshifts of ~6-8. WFC3 was specifically intended for detection of such systems in the 0.8-1.2 micron region, where ground-based observations are difficult due to atmospheric spectral features. o Synoptic observations of planetary atmospheres and surfaces at high resolution. o Laying the scientific groundwork for the JWST mission by undertaking observations of the brighter targets of interest to JWST which are below the observing threshold from the ground. It is inevitable that deployment of WFC3 on a platform smaller than HST would involve a significant descope in scientific productivity. Based on long discussions, and consultations concerning alternative uses of WFC3, here is our list of deployment options in priority order: (1) SM4. Since NASA has now commissioned an independent study of the safety issues surrounding a servicing mission, it is possible that SM4 will be resurrected. This is obviously by far the highest priority option. As long as SM4 remains a possibility, it is essential that no steps be taken that would compromise the specified performance of WFC3 or the schedule on which it could be made ready for SM4. Compared to other options, the costs and technical feasibility of SM4 are well established, and this is now probably the cheapest way of deploying WFC3. (2) Non-Shuttle servicing of HST. The most interesting possibility here is robot servicing using an enhanced version of the deorbiting propulsion unit (about $300M) which NASA is already developing. This could carry gyros and batteries which, operated from the attached external unit, could extend HST science operations for a number of years. It should be feasible to remove WFPC2 and install WFC3 with such a robot unit because only two bolts must be loosened and retightened. Internal rails and latches insure optical alignment. A single mating connector links in power and communications. There are no obvious serious technical obstacles, and add-on costs might not exceed those of a MIDEX mission yet would provide much greater scientific return. If Shuttle servicing is found not to be possible, SOC strongly recommends that NASA urgently explore all possible avenues for placing WFC3 on HST by other means. Robot servicing is a capability that must be of interest to the Moon-Mars initiative. (3) 2-m class fast-track telescope: As recommended by the Bahcall Committee (the "HST/JWST Transition Panel"), the best alternative to deployment on HST is to place WFC3 in a dedicated, 2-m class telescope on a schedule such that the "gap" between HST and JWST operations is filled. This would permit recovery of much of the WFC3 science, though the Design Reference Mission would have to be scrutinized for detailed compromises. This is likely technically feasible, but differential costs would probably exceed those of items (1) and (2). NASA has the option of making the fully characterized WFC3 hardware and documentation available for use in PI-class missions as "government furnished equipment." There is a broad spectrum of these, ranging from MIDEX-class ($150-200M) to Probe-class ($600M). These encompass areas where SOC has very limited expertise (e.g. planetary science, high energy astrophysics). PI-class science is typically very focussed, and these missions devote long observing periods to a narrow range of objectives. We concluded that a decrease in aperture to 1.0-1.5m in a PI-class mission would not support most of the unique science programs planned for HST/WFC3. We could not reach a consensus on a recommendation concerning PI-class missions. Some felt that SOC should not consider any option where the original prime science goals for the instrument could not be reached. Others argued that PI teams could well find good uses for WFC3, either as a finished unit or in the form of its qualified parts (i.e. flight components and spares). In particular, the mid-UV capability of WFC3 will remain valuable and unique through the end of the decade. All agreed that the value of WFC3 would depend on how quickly such alternate programs could be implemented. Because of these various potential channels for deployment of WFC3, we reiterate that it is imperative to complete the project's current plan for testing and documentation of the instrument. <<<<<<<<<<<<<<<<<<<<<<<<<<<< END <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<